The Law of Biot and Savart Law tells us how to find a differential form that generates the first de Rham cohomology of S3- embedded loop. Run a steady current through the loop. This form is just the dual of the induced magnetic field (using the Euclidean metric). Ampere's Law tells us that the form is closed. In fact, integration of the form over small cycles that lie in a tube around the circuit and are orthogonal to the current is 1 - so the form is a generator of the first cohomology. What physical phenomenon tells us the fundamental group of S3 - embedded loop?